New Journal of Glass and Ceramics, 2011, 1, 69-78
doi:10.4236/njgc.2011.12012 Published Online July 2011 (
Copyright © 2011 SciRes. NGJC
Physical Study of Thin Film and Monolithic
Nano-Composites [SiO2:11P2O5:3Al2O3:(1.2)Er
(1.2, 1.8 and 3)Yb] Prepared by Sol Gel Technique,
Planar Waveguide and Co-operative
Y. Badr1, I. K. Battisha2, A. M. S. El Nahrawy2, M. Kamal3
1National Institute of Laser Enhancement Sciences (NILES), Cairo University, Cairo, Egypt; 2National Research Center (NRC)
Department of Solid State Physics, Doki, Giza, Egypt; 3Physics Department El Manssoura University, Egypt.
Received May 21st, 2011; Revised June 18th, 2011; Accepted June 25th, 2011.
Nano-composite silica-phosphate system (SiO2-P2O5) co-doped with Al2O3 as a host material and prepared by sol gel
technique in two forms monolith and thin film using multilayer spin-coating method were activated by Er3+ and Yb3+
ions as in the formula; [SiO2:11P2O5:3Al2O3:(1.2)Er:(1.2, 1.8 and 3)Yb]. The prepared samples have been synthesized
using tetra-ethyl-o rthosilicate (TEOS) and trieth yl-phosphate (TEP) as precursor sources o f silica and phosphorus ox-
ides. The microstructure and crystallinity of the prepared samples will be characterized by using x-ray diffraction
(XRD) which, imply that the crystallite sizes of [SiO2:11P2O5:3Al2O3:(1.2)Er:(1.2) Yb] at 500 for bo th thin fi lm and
monolith forms of the prepared samples were found to be equal to 35 and 33 nm, respectively. The refractive index
will be evaluated by measuring the normal transmission and specular reflection of the prepared samples. The photo-
luminescen ce prop erties ha ve ana lyzed in the visible waveleng th rang e between 500 and 800 nm a s a function o f sam-
ple composition.
Keywords: Sol-Gel, Silica-Phosphate, Rare Earth, XRD, Photoluminescence, Waveguide, Co-Operative Up-Conversion
1. Introduction
In the last decade, various technologies have been em-
ployed for the fabrication of silica (SiO2) based inte-
grated optics (IO) components and a broad variety of
silicate glass systems have been investigated. So sil-
ica-phosphate glasses doped with rare earth have been
favored in the development of integrated waveguide am-
plifiers, where the rare-earth concentration must be or-
ders of magnitude higher than in fibers [1]. Glasses syn-
thesized by the sol–gel method are promising matrices
for the formation of optical nano-composites. The use of
these nano-composites in optoelectronics, photonics and
fiber optics has opened up the new way for the develop-
ment of unique information systems with tunable char-
acteristics over a wide frequency range [2]. Sol-gel
processing, has been shown to be a relatively inexpen-
sive method to prepare such IO components [3,4], which
may allow the incorporation of RE ion concentrations
higher than those possible by conventional glass melting
methods, but at the same time the stronger ion-ion inter-
actions may reduce the RE fluorescence performance, by
decreasing its intensity and lifetime. Photonic materials
for optical amplifiers’ based on rare-earth (RE) ions such
as Er3+, are in wide use today, especially for dense
wavelength division multiplexing (DWDM) applications.
However, the small absorption cross sections of Er3+ ions
have become a limitation to the optimization of such
materials for optical amplification and, therefore, a
number of methods have been proposed to increase the
excitation efficiency of Er3+ ions [5]. It was previously
reported that, the wavelength of the main Er3+ ground-
state transition, 1.54 µm, coincides with the standard wave-
Physical Study of Thin Film and Monolithic Nano-Composites [SiO:11P O:3Al O:(1.2)Er(1.2, 1.8 and 3)Yb]
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length use in optical telecommunication systems deter-
mined by the quartz waveguide transparency window.
The Er3+ ion can also efficiently emit light at other dis-
crete wavelengths in the visible and near-IR spectral re-
gions determined by the structure of the excited states of
this ion as in our case in the present work [6]. Er-
bium-ytterbium (Er3+:Yb3+) doped fiber lasers and am-
plifiers show a growing potential for many applications
in different areas such as industry, light emitting devices,
communication, military and research [7-9]. In order to
improve the luminescence performance of Er3+ ions
doped sol-gel silica-phosphate planar waveguides, co-
doping achieved with Al [10,11]. However, it would be
difficult to enhance the emission efficiency of Er3+ ions
due to its low absorption cross-section. A good alterna-
tive method to overcome this problem is to co-dope Yb3+
with Er3+ into a material. The ytterbium ion has a strong
absorption so it can use as a sensitizer for other lumines-
cent ions. Co-doping with Yb3+ has been shown to in-
crease the photoluminescence (PL) emitted by the rare
earth like Er3+ ions [12].
In the present work a preliminary study of silica-
phosphate co-doped with Al3+ ions as a host material,
activated by doping it with constant concentration of Er3+
ions at 1.2 mol% and different concentrations of Yb3+
ions at (1.2, 1.8 and 3) mol%, respectively and prepared
by sol-gel technique in two different forms thin film and
monolith. The results investigated using XRD, in order
to assess the structural properties. The photolumines-
cence of the prepared samples in the visible and infrared
wavelengths ranges will compared and evaluated. The
co-operative up-conversion emission spectra exhibited
the green emission bands assigned to 2H11/24I15/2 and
4S3/24I15/2 transitions and group red emission bands
between 600 nm and 800 nm that were attributed to the
4F9/24I15/2 transitions of Er3+ ions, respectively was de-
tected. All obtained data will be analyzed and compared.
2. Experimental
Silica-phosphate (SiO2: 11P2O5) doped with 3 mol% Al3+
ions, as a host materials was prepared by sol-gel tech-
nique in two different forms monolithic and thin film, it
is activated by constant concentration 1.2 mol% of Er3+
ions using the synthesizer Yb3+ ions at different concen-
trations (1.2, 1.8 & 3 mol%) planar wave guide. The
prepared samples were obtained by hydrolysis and
poly-condensation of tetraethoxysilane (CH3CH2OH)4Si
(TEOS, 99.999%, Sigma-Aldrich) as SiO2 precursor and
Triethyl-phosphate (C2H5O)3P(O) as P2O5 precursor in
ethanol. The solution were hydrolyzed under vigorous
stirring with distilled H2O containing HCl, which is used
Silica-phosphate (SiO
Aging one week at RT
then dried at 60
Heat treatment of monolithic
Heat treated at different
Thin film
Figure 1. Flow chart for the preparation of monolithic and
thin film [SiO2: 11P2O5: 3Al2O3: (1.2) Er (1.2, 1.8 and 3)
Yb], using sol gel method.
as a catalyst as described in Figure 1. In the case of
doping with the Er3+ and Yb3+ ions all preceding experi-
mental steps as-synthesized sol was then doped with 3
mol% Al(NO3)3-H2O, to aid in eliminating the presence
of hy droxyl groups and also favor the dispersion of
doping ions in the matrix. Then the Er3+ and Yb3+ ions
were introduced in the process, by dissolving Er
(NO3)3-H2O and Yb(NO3)3-H2O solutions in to the pre-
ceding mixture precursors with molar ratios 1.2 mol%
Er3+ and (1.2, 1.8 and 3 mol%) Yb3+, respectively. These
solutions then filtered, followed by stirring for one hour
at room temperature RT. The resultant homogeneous
solutions of monolithic materials filled in molds and
aged in RT for one week before dried in the oven type
GFL 71.5, at about 60 for 21 days until no shrinkage
appears. The final products were monolithic samples.
Samples were clear, transparent, with faint rose color and
without cracks. Densification of gel obtained by anneal-
ing in air for 3 h at temperature ranging from 100˚C up
to 900˚C in a muffle furnace with heating rate 1.5/min.
Preliminary crystallization obtained by heating the sam-
ples at 300 for 3 hours. In case of the thin film optical
treated silica substrates and glass substrates were used as
substrates for the deposition of silica-phosphate doped
with (Er3+:Yb3+) solution, using the same solution as for
the preparation of monolithic. This solution dispersed on
the substrate and then spun at 3500 rev./min for 30 sec-
onds in a clean room by using the spin coating. At least
two successive coatings were required to provide suitable
effective film thickness. After finishing the coating pro-
cedure, the substrates dried for 30 min at 600 and then
heat-treated at different heat treatment temperature from
100 up to 5000, giving crack free, homogeneous
and transparent enough for waveguide thin films, respec-
opyright © 2011 SciRes. NGJC
Physical Study of Thin Film and Monolithic Nano-Composites [SiO2:11P2O5:3Al2O3:(1.2)Er(1.2, 1.8 and 3)Yb]
Prepared by Sol Gel Technique, Planar Waveguide and Co-operative Up-Conversion
Copyright © 2011 SciRes. NGJC
X-ray diffraction (XRD) patterns from the prepared
samples were recorded with Philips X-ray diffractometer
PW/1710; with Ni filter, with monochromatised CuK
radiation of wavelength 1.54045 Å at 40 KV and 30 mA.
Crystallite sizes G were determined from the Scherrer’s
(G = K
is the wavelength, and D is the (corrected) full
width (in radians) of the peak at half maximum (FWHM)
intensity. The correction to the measured FWHM Ds for
a sample peak was made to accommodate systematic in-
strumental broadening and utilized peak widths Dq
measured from a diffraction scan, taken under identical
conditions, from a strain-free powdered quartz sample,
with crystallite size ranging between 5 and 10 lm. The
corrected sample peak widths were calculated as
(D = Ds2Dk2)1/2
Micro-strain and crystallite size contributions to D
separated using the Win-Fit program, using standard
samples for estimation of instrumental broadening. The
final sample crystallite sizes G obtained by Fourier
analysis, using the corrected profile. Nearly normal
transmittance and reflectance spectra were done by Jasco
V-570 spectrophotometer, in wavelength range (0.2 - 2.5
µm). The transmission electron microscope (TEM) al-
lows the user to determine the internal structure of mate-
rials. TEM was performed by using a JEOL JEM-1230
operating at 120 KV attached to CCD camera.
For photoluminescence (PL) measurement, the sample
excited by the 488 nm line of a Spectra Physics 2017
Argon laser used to excite room temperature lumines-
cence spectra. A fiber optic probe coupled to a Dilor Su-
perhead, equipped with a suitable notch filter, employed.
The scattered signal analyzed by a Jobin-Yvon HR 460
mono-chromator and a spectrum one CCD detector. A
150 line/mm grating used to collect the laser-excited
luminescence spectra, whilst for high-resolution lumi-
nescence spectra a 1200 lines/mm grating employed. The
PL emission obtained using lock-in amplifier (SR 510-
Stanford) technique and recorded by computer. The
measurements performed at room temperature.
3. Results and Discussion
3.1. XRD Results
Figures 2 and 3 show the XRD patterns of mono-
lithic(SiO2:11P2O5:3Al2O3:1.2Er2O3) doped with dif-
ferent concentrations of Yb3+ ions as in the formula(SiO2:
11P2O5:3Al2O3:(1.2)Er(1.2, 1.8 and 3)Yb), sintered at
different heat treatment temperatures (100˚C, 300˚C and
10 20 30 40 50 60 70 80
(A )
10 20 30 40 50 60 70 80
p Si3(PO4)4
Intensity (a .u.)
Figure 2 (A, B). XRD patterns of monolithic SiO2:11P2O5:3Al2O3 doped with (a) 1.2Er3+:1.2Yb3+ (b) 1.2Er3+:1.8Yb3+and (c)
1.2Er3+:3Yb3+, sintered at (A) 100˚C and (B) 300˚C for 3 h; p Si3(PO4)4 phase, * Si5P6O25 phase and • SiP2O7 phase.
Figure 3 (a, b and c). XRD patterns of monolithic SiO2:11P2O5:3Al2O3 doped with (a) 1.2 Er3+:1.2Yb3+ (b) 1.2Er3+:1.8Yb3+
nd (c) 1.2Er3+: 3Yb3+, sintered at 700˚C for 3 h; p Si3(PO4)4 phase, * Si5P6O25 phase, Er3SiPO9 phase and • SiP2O7phase. a
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700˚C) for 3 h. When silica-phosphate doped with (Er3+:
Yb3+) ions subjected to heat treatment for densification,
many properties of the gel changed as a result of struc-
tural changes in the host skeleton of a gel which, is at-
tributed to the development of cross-linking of the Si-O
and P-O bonds due to dehydration poly- condensation of
the system. The curves sintered at 100˚C show broad
hump at 2
between 18˚ and 30˚ attributed to amorphous
matrix. By increasing the temperature up to 300˚C very
weak peaks of silica-phosphate begin to appear due to
the presence of silica-phosphate nanocompounds. As-
signed to (hexagonal silica phosphate) Si3(PO4)4 and
(rhombohedra silica phosphate) Si5P6O25 phases accord-
ing to JCPDS cards- number (22 - 1380) and (70 - 2071).
These phases consists of isolated SiO6 and Si2O7 units
linked by PO4 groups in the system silica-phosphate
[13-15] to form SiO2-P2O5 nano- composite [16,17] in
addition of the presence of monoclinic silica phosphate
(SiP2O7) phase according to JCPDS card number (71 -
2073). Above 300˚C, the crystallization in silica-pho-
sphate gel glasses greatly changed the coordination of
Er3+:Yb3+ ions. An Er3+:Yb3+ ions situated in a binary
system composed of crystalline and glass phase. Another
effect of increasing the temperature of the samples is that
the intensity of the XRD peaks increased due to the con-
tinually change in the chemical structure and the rear-
rangements of the crystalline system. Then the prepared
samples become crystalline, with separation of the
phases; according to the diffraction peaks as shown in
Figure 3. By increasing the sintering temperature up to
700˚C, the intensity of XRD patterns increase giving rise
to crystallinity enhancement. Separation of the phases;
according to the diffraction peaks, the (hexagonal sil-
ica-phosphate) Si3(PO4)4 phase was eliminated by in-
creasing the temperature and the (rhombohedra silica
phosphate) Si5P6O25, (silica phosphate) SiP2O7 phases
increase and a new phase ( monoclinic erbium silica
phosphate) Er3SiPO9 appeared due to the effect of the
Er3+ ions, according to JCPDS cards no.(49 - 0206).
Figures 4 and 5 show the XRD patterns for some thin
films silica-phosphate system co-doped 3 mol% Al2O3
with 1.2 mol% Er3+:(1.2 & 1.8)Yb3+ ions samples as in
the following formula; (SiO2:11P2O5:3Al2O3:1.2Er2O3:
(1.2 & 1.8)Yb2O3) prepared from the same precursors,
sintered at different heat treatment temperatures, 100˚C,
150˚C, and 500˚C for 3 h. The behavior of the prepared
thin film samples after dried at low sintered temperature
100˚C and 150˚C, give nearly the same trend of the
monolithic samples observed where the samples were
still in the amorphous state and have larger specific area.
By increasing the sintered heat treatment temperature up
to 500˚C, the intensities of the Si3(PO4)4, Si5P6O25 and
SiP2O7 phases increase with increasing the sintering heat
treatment temperature. While, the initial state of a film
generally denser and less cross-linked than a bulk gel
made from the same sol, and this transport path of heat
through the thickness of the film. Where, these films
have been prepared from the same precursor of preparing
the monolith samples by aging two days after spinning.
The observed change in the XRD peaks height as well as
the broadening could interpreted by the adsorption of the
incorporated atoms on the surface of the growing sil-
ica-phosphate doped with REEs gel microcrystal. The
thinner of the film thickness may be preventing it to
grow larger along or perpendicular to the substrate com-
pared with the monolithic form samples. We found that
the crystallizations growth in the thin film was faster and
more intense due to the thinner thin film than the mono-
lithic, where the film is denser and has smaller pores,
Figure of XRD of monolith sample sintered at heat
treatment temperature 500˚C not shown here due to the
large number of figures presented.
By confirming the crystallite size data calculated by
Scherrer’s equation (G = K
), and by using the
Win-fit programmer for [SiO2:11P2O5:3Al2O3:(1.2)Er
(1.2)Yb] at constant sintering temperature 500˚C for both
thin film and monolith the crystallite sizes were found to
be equal to 35 and 33 nm, respectively [18-21].
3.2. Optical Properties
Figure 6(A) and (B) show the optical transmission and
reflection spectra of the investigated (A) [SiO2:11P2O5:
3Al2O3:(1.2)Er(1.2, 1.8 and 3)Yb] and (B) [SiO2:11P2O5:
3Al2O3:(1.2)Er(1.8)Yb] thin film sintered at 100˚C for
the former and at different heat treatment temperature
300˚C and 700˚C for the later. The film deposited on
glass and optical treated silica substrates. The transmit-
tance data corrected relative to the optically identical
uncoated substrate. It was observed that the transmission
showed lower interference fringes that are disturbed by
the absorption of OH in silica-phosphate doped with
(Er3+:Yb3+) ions while higher transmittance was obtained
at lower temperature. The OH eliminated by increasing
the sintered heat treatment temperature. This indicates
that the optical path of silica-phosphate glass and doped
with some Er3+ and Yb3+ ions increases by increasing
temperature. Furthermore, the transmitted intensity de-
creases with increasing temperature, mainly due to the
light scattering increased in silica-phosphate doped sam-
ples and might be due to the poly-condensation
and densification produced by increasing the sintered
temperature, resulting in changing the faint rose color
tobe dark rose as discussed in the experimental part Sec-
ion 2. This result is in agreement with XRD results ob- t
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10 20 30 40 50 6070 80
(A )
10 2030 405060 7080
p Si3(PO4)4
Figure 4 (A, B). XRD patterns of thin film SiO2:11P2O5:3Al2O3 doped with (a) 1.2Er3+:1.2Yb3+ and (b) 1.2Er3+:1.8Yb3+, sin-
tered at (A) 100˚C and (B) 150˚C for 3h; p Si3(PO4)4 phase, * Si5P6O25 phase.
10 20 30 40 50 60 70
Intensity (a.u.)
p Si3(PO4)4
Figure 5. XRD patterns of thin film SiO2: 11P2O5:3Al2O3 doped with (a) 1.2Er3+: 1.2Yb3+ and (b) 1.2Er3+: 1.8Yb3+, sintered at
500˚C for 3 h; p Si3(PO4)4 phase, * Si5P6O25 phase, • SiP2O7 phase.
tained in the present work.
The behavior of the refractive index (n) for (SiO2:
11P2O5:3Al2O3:(1.2)Er:(1.2, 1.8 and 3)Yb), sintered at
different temperature ranging from 100˚C up to 700˚C
was shown in Figure 7. By increasing the sintering tem-
perature and the concentration of the synthesizer Yb3+
ions the refractive index increases due to the increase in
the crystallization degree. The sample presents a good
variation of the refractive index illus trating the prepara-
tion of a single mode silica-phosphateglasses doped with
Er3+:Yb3+ ions planar waveguide. The refractive index
linearly increased with increasing densification, conden-
sation, temperature and increasing the Yb3+ ions concen-
trations indicated the change in chemical structure and
the rearrangement of the host sample when incorporated
ith different Er3+: w
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4006008001000 1200
T, R %
w a velength(nm )
Transm ission
Reflec tio n
4006008001000 1200
T, R %
Figure 6 (A, B). Optical transmission & reflection spectra for (A) [SiO2:11P2O5:3Al2O3:(1.2)Er: ((a) 1.2), (b) 1.8 and (c) 3
Yb], all sintered at 100˚C and (B) [SiO2:11P2O5:3Al2O3:(1.2) Er:(1.8)Yb], sintered at heat temperature (A) 300˚C and (B)
Yb3+ ions concentration [22,23]. This creates a more
rigid network and causes a decrease in the molar volume,
leading to higher refractive index [24].The values of re-
fractive index (n) of thin film samples are given at
wavelength = 500 nm. It was found that it increases by
increasing the sintered temperature and the Yb3+ions
concentration ranging between the following values 1.55
up to 1.68 for silica-phosphate doped with Er3+:Yb3+ ions
and increasing temperature as shown in Table 1 and
Figure 7. This increase is associated with the condensa-
tion and densification of the materials, which enhanced
by doping the silica-phosphate with different REEs ions
and increasing temperature. The obtained data allow the
preparation of low loss coupling systems planar wave-
guide [25]. The refractive index (n) at wavelength = 500
nm of [SiO2:11P2O5] thin film and monolith samples
sintered at 500˚C were equal to 1.65 and 1.59, respec-
3.3. Photoluminescence Spectra
Figures 8 and 9 show the photoluminescence (PL) emis-
sion spectra of monolithic and thin film samples as in the
following formula [SiO2:11P2O5:3Al2O3:(1.2)Er: (a)
1.2Yb and (b) 3Yb], both sintered at temperature 200˚C.
It is well known that the absorption cross-section of Er3+
ions is small, for that Yb3+ ions was used as a sensitizer
to increase the Er3+ ions PL emission under Argon laser
excitation at wavelength (488 nm) [12,26]. It has been
well addressed that the green emissions at 542, 552 and
571 nm have been attributed to the intra-4F-transitions
Table 1. The values of refractive index for thin film [SiO2:
11P2O5:3Al2O3:(1.2)Er:(1.2, 1.8 and 3Yb], sintered at dif-
ferent temperature.
Samples(SiO2:11P2O5:1.2Er2O3:(1.2, 1.8 & 3)Yb2O3:3Al2O3)
T˚C 1.2Er3+:1.2Yb3+ 1.2Er3+: 1.8Yb3+ 1.2Er3+: 3Yb3+
100 1.55 1.57 1.59
200 1.56 1.59 1.61
300 1.58 1.61 1.63
500 1.61 1.63 1.65
700 1.64 1.66 1.68
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100 200 300 400 500 600 700
Refractive ind ex (n)
Tem perature ( 0C)
Figure 7. The refractive index as a function with temperature for thin film (SiO2:11P2O5:3Al2O3:1.2Er) doped with different
concentrations of Yb ions (a) 1.2 (b) 1.8 and (c) 3 mol%, sintered at different temperature.
Figure 8. The room-temperature visible and NIR emission spectra of the monolith [SiO2:11P2O5:3Al2O3:(1.2)Er:((a) 1.2 and
(b) 1.8)Yb], sintering at temperatures 200˚C.
600620 640 660 680 700
600 620640 660 680 70
W avelength (nm )
Intensity (a.u.)
Figure 9. Room-temperature PL emission spectrum of thin film (SiO2:11P2O5:3Al2O3:1.2Er2O3) doped with two different
oncentrations of Yb2O3 (a) 1.2 (b) 1.8 mol%, sintered at temperature, 200˚C. c
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of Er3+ ions and were assigned to the (4S3/24I15/2 ) (542
and 571 nm) and (2H11/24I15/2) (542 nm) respectively
for monolithic sample. The group red emission is attrib-
uted to a transition of Er3+ ions assigned to (4F9/24I15/2 )
in region between 600 and 800 nm with higher intensity
in both form of samples thin film and monolith at (666
nm), which is dominant in all spectra [27]. In low sinter-
ing temperature the Er3+ ions doping has multiplicity of
the sites and environments due to the disordered nature
of Er3+ ions located in the multi-phases. To compare be-
tween the green and red PL emission we can propose two
mechanisms; first one, for dominant green luminescence
in which, the laser light brings the Er3+ ion in to 4I9/2
level, which then decays through a non-radiative process
into the 4I11/2 metastable levels and subsequently into the
4I13/2 metastable level. Energy transfer processes bring
the Er3+ ion into (4F7/2) state from which (4S3/2) is popu-
lated through the non-radiative relaxation. The second
mechanism for the dominant red luminescence one is
that the laser beam brings the Er3+ ion to the excited state
4I9/2 level. One ion non-radiatively decays to the 4I11/2
metastable level, and the second decays to the 4I13/2 me-
tastable levels. Energy transfer processes bring the Er3+
ion to the 4F9/2 and a red emission can observed. The
spin-allowed radiative transition from the preceding lev-
els to the ground state gives rise to the visible and red PL
emissions, respectively. The energy transfer (ET) be-
tween two close ions also takes place and plays a sig-
nificant role in the PL emission. It was observed that the
4F9/2 is predominantly excited in this material with the
high intensity of the 4F9/2 4I15 transition. The absorp-
tion 488 nm radiation results in the 4I11/2 (Er) level, with
population proportional to the pump power. The
de-excitation of the 4I11/2 (Er) level, via no-radiation
multi-phonon relaxation, takes the population of the 4I13/2
(Er) level. The absorption of the second photon ( 488
nm) promotes the excitation in the 4F9/2 (Er) level, re-
sulting in the group red emission with its maximum at (
666 nm) [28]. The ESA approach occurs only during
excitation, whereas the ET can happen both during and
after excitation.
The red emission is much stronger than green emis-
sions, which may be due to effect of doping the prepared
samples with Yb3+ ions and the intense of the spectra
increased with increasing the Yb3+ concentrations. The
introduction of Yb3+ in silica-phosphate host brings great
changes for the photoluminescence properties of Er3+
ions and a moderate green to red light can be seen in
monolithic sample under the same excitation. Where the
multiplicity of RE sites in the host matrix are known to
enhance the inhomogeneous broadening of the emission
and absorption lines [29,30] and a red shift was observed
for the emission lines. Once Er3+ and Yb3+ ions were
excited, they relaxed to ground state, emitting the infra-
red emissions. The emission of ytterbium was cross-
relaxed and the electrons in the 4I11/2 level of erbium in-
creased their energy to the 2F7/2 level [31]. In order to
improve the photoluminescence performance of Er3+
doped sol-gel silicate planar waveguides, co-doping
achieved with Yb and Al or P [29,31]. The RE ion Yb3+
is known to have a significant sensitizing effect on Er3+
ions doped glasses [12,32], are attributed to the intra f-f
transitions of Er3+ And Yb3+ ions. Some of emissions
bands in visible region were disappeared in thin film
sample, due to easy elimination of OH- groups and the
densification resulting in the rearrangement of the struc-
3.4. Co-Operative Up-Conversion
Emission of Monolithic
[SiO2:11P2O5:3Al2O3:1.2 Er:1.8Yb]
The effect of another existing source on the monolithic
(SiO2:11P2O5:3Al2O3:1.2Er:1.8Yb) sample using the
laser diodes with excitation at 808 nm presented as fol-
low in Figure. 10, which shows the room temperature
co-operative up-conversion spectra of the monolithic
[SiO2:11P2O5:3Al2O3:1.2Er:1.8Yb], sintered at tempera-
ture 300˚C. The green emission in the range between 550
and 570 nm attributed to the 4S3/24I15/2 transition. The
visible up-conversion emission band at 589 nm is the
maximum one, which can attributed to the 4S3/2 4I15/2
transition of Er3+ ions and a group red emission in the
region between 600 - 650 nm assigned to another intra-4f
transition 4F9/24I15/2.
The up-conversion emission of Er3+ and Yb3+ions can
be explained by several well-known mechanisms such as
excited-state absorption (ESA) previously reported [32]
as shown in Figure. 11 and energy transfer up-conver-
Figure 10 Room temperature Co-operative up-conversion
emission spectra under laser diode excitation at 808 nm
from monolithic [SiO2:11P2O5:3Al2O3:1.2Er:1.8Yb], sin-
tering at 300˚C.
opyright © 2011 SciRes. NGJC
Physical Study of Thin Film and Monolithic Nano-Composites [SiO:11P O:3Al O:(1.2)Er(1.2, 1.8 and 3)Yb] 77
22 523
Prepared by Sol Gel Technique, Planar Waveguide and Co-operative Up-Conversion
sion (ETU). The ETU involves not only two closely
neighboring Er3+ ions but also Er3+ and Yb3+ ions. When
Yb3+ at 4F5/2 state returns non-radiatively to the 4F7/2
ground state, its energy is transferred to neighboring Er3+
in the 4I11/2 state, and then this Er3+ ion was excited to the
4F7/2 (2H11/2) state through the following channels: 4I11/2
4F7/2 and 4I13/2 4F9/2. This is the main pathway by
which Yb3+ sensitizes the up-conversion process.
After wards, excited Er3+ ions at 4I13/2 level will take
one ion to the 4I9/2 level. This step followed by other
successive transfer processes from ions at the 4I13/2 state,
which results in the excitation to higher levels. After
non-radiative decay to lower states, radiative transitions
to the ground state give rise to the observed red
up-converted fluorescence [32].
4. Conclusions
Nano-composite silica-phosphate glasses activated by
Er3+: Yb3+ ions planar waveguides [SiO2:11P2O5:3Al2O3:
1.2Er:(1.2, 1.8 and 3)Yb] were successfully prepared by
sol–gel technique, in two forms monolithic and thin film
by using spin-coating method. This as-synthesized sol
was doped with 3 mol% Al3+ ions, to eliminate the OH
groups and to increase the solubility of Re3+ ions. The
structure of the prepared samples was evaluated by using
XRD. One can conclude that the degree of crystallinity
and the crystallite sizes of the trivalent Er3+ and Yb3+
ions dispersed in silica-phosphate host samples as thin
film and monolith were increased by increasing both the
concentrations of Er3+ and Yb3+ ions, and the increase in
the sintering heat treatment temperature.
The values of the refractive index (n) of thin film sam-
ples are given at wavelength = 500 nm. It was found that
it increase by increasing the sintering temperature and the
Figure 11. The energy level diagram of the green and red
up-conversion emissions from the Er3+ and Yb3+ ions [32]
Yb3+ ions concentration from 1.55 up to 1.68. The ob-
tained data allow the preparation of low loss coupling
systems planar waveguide.
The visible and red Photoluminescence implies that
the position of the emission peaks in the spectra corre-
sponding to excitation by Argon laser light with wave-
length 488 nm. It was due to transitions inside erbium
ions corresponding to intra-4f transition of Er3+ and Yb3+
ions assigned to 2H11/24I15/2, 4S3/2 4I15/2 and 4F9/24I15/2
for the monolith and thin film silica –phosphate planar
wave guide. The red emissions in region between 600 -
700 nm are assigned to 4
F 9/24I15/2 transitions of Er3+
ions and its intensity increased with increasing the con-
centrations of Yb3+ ions in case of monolithic sample.
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